Program providers such as television networks and stations, studios, Internet broadcasters and service providers, cable operators, satellite operators, and the like, deliver video content to consumers via digital signals. Devices and signals involved in the delivery of video content to consumers may comply with various industry specifications, or standards, which have been promulgated by groups desiring, among other things, to ensure interoperability between systems and devices that deliver the video content, and to ensure that the video content is not copied or otherwise misused.
The Digital Display Working Group (“DDWG”), for example, has published a document entitled Digital Visual Interface, Revision 1.0 (the “DVI Specification”), which sets forth an industry standard for a physical digital visual interface (“DVI”), and a protocol for electrical signaling thereon, between a source device (such as a PC, a set-top box, a DVD player, or a digital VCR) and a display device (such as a television monitor, a computer monitor, or a projector). The DVI Specification is hereby incorporated by reference in its entirety for all purposes, as if set forth in full herein.
Digital Content Protection, LLC developed the High-bandwidth Digital Content Protection System (the “HDCP System”), which provides protection against copying for audiovisual content (as defined in the United States Copyright Act as in effect on Jan. 1, 1978) transmitted over certain high-bandwidth interfaces, such as DVIs, and has promulgated a standard describing the HDCP System, entitled High-bandwidth Digital Content Protection System, Revision 1.00 (the “HDCP Specification”). The HDCP Specification is also hereby incorporated by reference in its entirety for all purposes, as if set forth in full herein.
One element of the HDCP System is an authentication protocol, through which HDCP/DVI-enabled source devices (referred to as HDCP transmitters) verify that HDCP/DVI-enabled display devices (referred to as HDCP receivers) are licensed to receive HDCP content. A second element of the HDCP System is the transmission of encrypted content between an HDCP transmitter and an HDCP receiver based on shared secrets established during the authentication protocol.
One method the HDCP System uses to identify unauthorized or compromised devices is to require that both the HDCP transmitter and the HDCP receiver periodically calculate certain authentication values when encrypted content is being transmitted-the authentication values must correlate and be received in a timely manner to maintain communication between the HDCP transmitter and the HDCP receiver. When authenticated communication between the HDCP transmitter and HDCP receiver is lost, a period of “snow” generally appears on the HDCP receiver.
One problem not adequately addressed by the HDCP Specification, however, is that the loss of authenticated communication between HDCP transmitters and HDCP receivers can occur merely when the transmitted content changes formats, because different formats may have different timing parameters. For example, timing parameters such as refresh rates (the number of times per second an HDCP receiver paints a screen with a video signal) affect the timing of vertical blanking intervals (the short spans of time between screen paintings), which are used to calculate and/or correlate certain authentication values. When a new format has a slower refresh rate than the original format, for example, the HDCP transmitter and HDCP receiver may lose authenticated communication, and snow may appear on the HDCP receiver. Frequent disruption in video reception may cause consumers to become dissatisfied with the performance of their source devices, display devices, and/or content providers.
There are, therefore, needs for methods and apparatuses for transmitting content to HDCP receivers that allow for content formats to change without disrupting video reception by the HDCP receivers.